The present invention is directed toward magnetic recording heads and, more particularly, toward perpendicular magnetic recording heads having an improved write field gradient.
The ability to increase the storage capacity in magnetic recording is an ongoing concern. As the amount of information to be stored continues to increase, demands for higher density recording also continue to increase. In conventional longitudinal magnetic recording systems, as areal densities approach 100 Gbit/in2 it has become increasingly difficult to meet the requirements of thermal stability (the degradation of written information due to thermal fluctuations), SNR (Signal-To-Noise Ratio) and writeability. Perpendicular recording is considered as one of the possibilities to achieve ultrahigh areal densities beyond conventional longitudinal recording.
Ultrahigh areal densities can be obtained in a perpendicular recording system by increasing the linear and/or track densities. For high linear densities, the transition parameter of a bit transition, as well as the transition jitter, need to be minimized. The actual values of the transition parameter and the transition jitter will depend upon both the properties of the recording medium and the on-track field gradient of the write head. In an ideal case, the write field gradient should be a step, i.e., an infinite slope of the field gradient, at the dynamic coercivity of the recording medium being used. In a similar manner, the track density that can be obtained will depend, in part, on the off-track field gradient of the write head.
One perpendicular recording system configuration, shown in FIG. 1, uses a single pole write head with a wide return pole and a recording medium which includes a magnetically soft underlayer and a magnetically hard recording layer, conventionally known as a double layered recording medium. As shown in FIG. 1, the magnetic recording head 10 has a single (main) pole 12 for generating a field at the recording media 14, and is conventionally known as a single pole magnetic recording head. The magnetic recording head 10 includes the main pole 12, a return pole 16 and a magnetic via 18 connecting the main 12 and return 16 poles. An electrically conductive magnetizing coil 20 surrounds the magnetic via 18.
The recording media 14 typically includes a substrate 22, a soft magnetic underlayer 24 formed on the substrate 22 and a perpendicularly magnetized recording layer 26 on top of the soft underlayer 24. Additionally, the recording media 14 includes a spacing layer 28 between the soft underlayer 24 and the recording layer 26, and thin layers of carbon overcoat 30 and lubricant 32 on top of the recording layer 26. The carbon layer 30 is applied to the magnetic recording layer 26 and protects the magnetic recording layer 26 against damage from direct contact with the read/write head, and also serves as a corrosion barrier to prevent oxidation of the magnetic recording layer 26. The lubricant layer 32 is applied to the carbon layer 30 and has viscous properties to produce sheer stresses between the read/write head and disc during contact.
When writing, the magnetic recording head 10 is separated from the recording media 14 by a distance conventionally known as the xe2x80x9cfly heightxe2x80x9d. The recording media 14 is moved past the magnetic recording head 10 such that the recording head 10 follows the tracks of the recording media 14. The track of the recording medium 26 on which information is being recorded in FIG. 3 is denoted by 26xe2x80x2. The coil 20 is traversed by a current and produces a magnetic flux 34 which is channeled by the main pole 12 to produce an intense writing flux at the tip 36 of the main pole 12 which records the information in the magnetic recording layer 26xe2x80x2. The flux 34 passes from the tip 36 of the main pole 12, through the magnetic recording layer 26xe2x80x2, into the soft underlayer 24, and across to the return pole 16, which provides a return path for the flux 34. Thus, a closed magnetic circuit is formed in which the magnetic flux in the recording layer 26xe2x80x2 directly under the poles 12, 16 of the magnetic recording head 10 is oriented perpendicular to the plane of the recording layer 26. The cross-sectional area of the return pole 16 is larger than that of the main pole 12 to ensure that the flux density at the return pole 16 is sufficiently reduced as not to magnetize the recording layer 26xe2x80x2.
By way of example, a perpendicular recording system proposed for an areal density of 100 Gbit/in2 uses a single pole write (main) head 12 having a width of 130 nm and a thickness of 300 nm. A hard recording layer 26 thickness of 16 nm typically yields a total soft underlayer 24 to main pole 12 spacing of about 35 nm (which includes the spacing layer 28, the overcoat 30, the lubricant 32 and air).
As a consequence of the relatively large 35 nm spacing between the main pole 12 and the soft underlayer 24 as compared to the main pole 12 width of 130 nm and pole height of 300 nm, the maximum field in the write gap is reduced significantly from 4 xcfx80Ms, the saturation magnetic flux density of the main pole 12. FIG. 2 illustrates a maximal on-track field (Hy) of about 1.2 Tesla for the conventional recording head 10 using a saturation magnetic flux density value of 2.0 Tesla. This results in a reduced write on- and off-track field gradient for recording head 10. An additional consequence of the significant write gap relative to the dimensions of the main pole 12 is that the flux from the sides of the main pole 12 which are recessed from air bearing surface of the main pole 12 will contribute to the field at the write gap. This additional flux will degrade the write field gradient for both the on- and off-track directions. The flux arising from the magnetization at the air bearing surface of the main pole 12, as well as from the sides of the main pole 12, is schematically illustrated in FIG. 3. The graph of FIG. 4 illustrates the magnitude of the flux from the sides of the main pole 12 as the sides become further recessed from the air bearing surface of the main pole 12. The general scaling trend of perpendicular recording towards Tbit/in2 is such that the write field gradient will further deteriorate as the reduction in spacing between the main pole 12 and the soft underlayer 24 is small relative to reductions in the main pole 12 width and height.
An integral aspect of perpendicular recording is that the write field at the tip of the main pole is mainly perpendicular to the plane of the recording layer. It is known that the writeability, as well as the writing speed, of a perpendicularly magnetized grain depends upon the angle of the applied field to its uniaxial anisotropy axis, with perfect anti-parallel alignment being the worst. A small, longitudinal field component in the write field gradient will increase the writeability and write speed for a perpendicularly oriented grain without degrading the transition parameter, as long as the write field is primarily perpendicular to the recording layer.
The present invention is directed toward overcoming one or more of the above-mentioned problems.
A single pole magnetic recording head is provided according to the present invention for perpendicular magnetic recording on a recording medium. The magnetic recording head includes a main magnetic pole, i.e., a single pole magnetic recording head, and a coil magnetically coupled to the main pole for magnetizing the main pole in a first magnetization direction. The magnetic recording head further includes a layer of ferromagnetic material anti-ferromagnetically coupled to the main pole such that magnetization of the ferromagnetic layer is in a second magnetization direction substantially anti-parallel to the first magnetization direction of the main pole.
In one form, the anti-ferromagnetic coupling is accomplished via an interlayer disposed between the main pole and the ferromagnetic layer. The interlayer and the ferromagnetic layer may be substantially the same shape as the main pole, or may be provided only at a pole tip region of the main pole. The interlayer provided between the ferromagnetic layer and the main pole may include a thin layer of ruthenium.
In another form, the interlayer and the ferromagnetic layer are provided only at a trailing edge of the main pole.
In a further form, the main pole and the ferromagnetic layer are each made of at least one material selected from the group of soft magnetic materials including at least one of Co, Fe and Ni. Additionally, the ferromagnetic layer may have a saturation magnetic flux density equal to or less than the saturation magnetic flux density of the main pole.
In yet a further form, the thickness of the main pole is greater than the thicknesses of the ferromagnetic layer and the interlayer.
It is an aspect of the present invention to improve the write field gradient for a perpendicular magnetic recording head in both the on-track and off-track directions.
Other aspects and advantages of the present invention can be obtained from a study of the specification, the drawings, and the appended claims.